Electric-furnace system



March 23 1926&\ 1,578,027

, J. w. HARSCH ELECTRIC FURNACE SYSTEM Filed Feb. 20, 1925 4 Sheets-Sheet 1 16 I ew Q INVENTO MMCOX;

1 ATTORNEY.

March 23 19266 7 J. w. HARSCH ELECTRIC FURNACE SYSTEM 4 Sheets-Sheet 2 mks/47v M2 z Filed Feb. 20, 1925 a romvsi March 23 1926. J. W. HARSCH ELECTRIC FURNACE SYSTEM 4 Sheets-Sheet 5 Filed Feb. 20, 1925 M my. $20

5 ATTORNEY.

J. w. HARSCH ELECTRIC FURNACE SYSTEM March 23 192s. 1,578,027

' Filed Feb. 20, 1925 4 Sheets-Sheet 4 I l F l 1 1 l 14 9 g V 1a in i 7% /wrok. BY M Q4 62% ATTORNEY.

' Patented Mar. 23,1926.

uNrrso STATES JOHN HARSGH, IPEILADELPHIA,

PENNSYIiVANIA, ASSIGNOR TO LEEDS &

NORTHRUP COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORJPORATION OF PENNSYLVANIA.

ELECTRIC-FURNACE SYSTEM.

Application filed. February 26, 1925. Serial No. 10,486.

To all whom it may concern:

Be it known that I, JOHN W. HAnscrr, a

citizen of the United States, residing in the city and county of Philadelphia, State'of Pennsylvania, have invented certainnew and useful Improvements in Electric-Furnace Systems, of which the following is a specification.

My invention relates to heating apparatus, such as furnaces, and more particularly electrically heated furnaces; and my invention relates to a method of operating the heating apparatus or furnace, and more particularly to a method of heat treatment of steel and kindred materials, as for example, for drawing or temperingsteel or the like.

In accordance with my invention, substantial uniformity of temperature throughout the heating chamber, and more particularlythroughout the contents thereof treated therein, and high rate of heating to bring the heating chamber and its contents rapidly up to a desired or control temperature without overshooting that temperature, are procured by effecting reversals of the convection or forced circulation within the heating chamber or furnace of the air or other gas therein. i Certain of the subject matter herein disclosed-but not claimed, and more particularly that not relating generally to the reversal of the direction of circulation of the air or gas-within thefurnace, is described and claimed in application Serial No. 65,- 715, filed by Irving B. Smith on October 30, 1925. 7

My invention resides in the method, system and apparatus of the character her'einafter described and claimed. v For an understanding of my method, and for an illustration. of some of the various forms my invention may take, reference is to be had to the accompanying drawings, in which:

Fig. 1 is a vertical sectional view, partly in elevation, of an electric furnace embodying my invention.

Fig. 2 is a horizontal sectional view, partly in plan, on the line 2-2 of Fig. 1.

Fig. 3 is a vertical sectional view of a modified form of furnace.

rig. 5 is a diagrammatic view comprising a part of the structure of Fig.4 and one of the circuit arrangements and controls utilizable in accordance with my invention;

7 Fig. 6 is a side elevational view of a motor and associated reversing mechanism.

Fig. 7 is a vertical sectional view, partly in elevation, on the line 7-7 of Fig. 6.

Fig. 8 is a cross section of a portion of the structure of Fig. 6.

Figs. 9 and 10 are vertical sectional views of a furnace adapted for convection circulation with parts in positions to cause circulation in opposite directions.

Fig. 11 is in part a horizontal section on line 11-11 of Fig. 9.

Referring to Figs. 1 and 2, there is shown a furnace or heat-treatingappartus F, adapted for forced circulation, comprising the metal jacket or housing 1, which may be cylindrical, secured at its lower end to the bottom member 2, carried by a frame having the legs 3. Disposed within and spaced from the jacket 1 is the shell or inner lining 4, whose bottom 5 is spaced from the bottom 2 by the blocks 6, through which extend conductivity. -The upper end of the lining v 4 is securedtov the annular member 10, surrounded-by the ring 11 of refractory material, which in turn is surrounded by the brick' ring 12, upon which latter rests the top annular casting 13, upon which is carried the support 14, to whichthere is pivoted at- 15 the arm 16, to which is pivoted at 17 the .lid or cover member 18, which may be be raised by pressing downwardly upon the lever 19, pivoted at 2 0 and engagingv the arm 16 to the left of its pivot 15. In so far as concerns some of the features of my invention, heat may be developed .within the furnace by any suitable method,

as bycombustion of gas or oil. In three generated electrical y by passage of current through the resistances or resistors 21 and 22 of any suitable type or character, either embedded in refractory material, or as illustrated, dis osed in the open within the furnace chain er adjacent the, inner-lining 4. As indicated, in Figs. 2 and 5, there are two sets of resistances, each comprising a plurality of parallel connected resislorsjor resistance conductors extending'vertically adjacent and insulated from the liiiiiig 4. Connections are made to the resistors through conductors having terminals in the terminal boxes 23 and 24. In the example illustrated, the resistance elements 21 and 22 are exposed to direct contact therewith gas within the furnace .hereinafter described, by passing current of the' air or other chamber.

Between the upper and lower rings 25 and 26 and the standards or inen'ibers 8 is secured the shell or: basket support 27,'ot'

sheet metal, preferably circumferential] y and vertically continuousor substantially uninterrupted by perforations or openings, to ex 29, having the eyes 29? for reception of crane hooks, and havingthe outwardly extending;

' flan e 30 resting upon the upper end of the shel 27 and membcrs'8. At its lower end the shell 28 is secured to the spider 31.

Disposed below the basket and its spider' 31 and forming a bottom-for the shell 27 is the conical orfunnel-shaped. member .32

secured'upon a ring or=pieces33 secured to the member 8.

Boltedto the bottom 2 is the fan shaft bearing-member 34:, in which is disposed the shaft 35, upon which is secured thepulle'y 36 driven through belt 37 by the pulley 38 se-,'

cured upon the shaft of the electric motor M, preferablfy reversible as hereinafter described, or driving the fan or blower 39,

' disposed at the-opening 40 at .tl'iebottom of the. member 32. Thebottom'fi ofthe finner linin 4 preferably deflects upwardly, as

at 41, to orm a passage leading to'the' lower sideofthefan39."

In the modification illustrated in Fig. '3, the overalliheight of the, structure is materiallydiminished by mountin the motor M u on the lid or cover18; w ich carries the I an. shaft 35' driven by the motor M,

preferabl reversible, and carrying atits ower 'en the propeller fan '39,.wliich with the motor M is removable as a lllllt'wltll the lid 18. Disposed above the fan is the downwardly 'e'xtending air-guiding surface 41',

" and :beneath thefan is disposed; the conical ,orfunnel-shaped' member, 32 carried by the upper ring 29 of the basket or work container 28. The openingAO of the member 32 is disposed adjacent the fan'tlf). I i

The work or material to be heated is placed within the basket 28, resting upon the lower grating or spider 31. The work may be a single piece, or a plurality of pieces either carefully or' symmetrically piled within t-liebasket or placed therein irrcgularly. For example, th'e contents of the basket may he a' plurality of gears of steel or a'lloy steel to receive heat treatment of any suitable character, for example, for drawing or tempering.

l/Vith the furnace cold, it is brought rapidly to the "desired temperature, as, for

example, a temperature of a .predetcrmmed magnitude at wliic.h the chamber is to be maintained, as by automatic control system through the setsof resistors 2i and 22 in parallel. During this preliminary stage of heating the fan 39 is driven by the motor M at suitable speed, effecting circulation of the hot-gases or airdownwardly between the shells {t and 27, past the'resistors 21 and 22, thence between the members 32 and 41 to the under side of the fan 39 which j't'orces the air or gases upwardly through the-member 32, spider 31,. through the basket or shell 28, upwardly through and between the gears or other pieces therein, and thence outwardly over the edge of the basket and thence downwardly again between the shells 4 and 27. This circulation of the heated air or gas serves to maintain the temperature rise substantially uniform throughout the basket and its contents and serves alsoto expedite r t the rise in temperatureof the furnace.

The fan 39 is from time to time, preferably periodically, and-preferably at relatively-short intervals, as Oftlle order of a minute or two, reversed, by. reversal of the direction of, rotation of the rotatable element of the motor M, or, ashereinafter described in connection, with Figs. 6-8, by

mechanical means] In either case, the direction of circulation of the air is from time to time-reversed, with the result that the temperature rise is substantially uniform throughout the contents of the basket and the furnace as a whole,

with the added advantage of increased 'uniformity .of heating and prevention of Y over-shooting of the temperature beyond the desired or predetermined control temperature, 'as compared with the cases where thereis no circulation, and compared also with.

the case where the circulation is always in -one direction.

- I have found that by so circulating the "air or gases within the furnace and by of footing reversal-of the direction of c'ireulation from time to-time, the temperature 'of the ,work or contents of the basket is for all.

. feetedby the heat treatment.

The desired uniformity of ten'iperature of the contents of the basket is the more readily .ingeffects due to radiant heat obtainable from the fact that the basket 28 or the shell 27, or both, intercept the radiant heat which would otherwise be absorbed by those parts of the contents lying adjacent the wall or shell '28, causing them locally to attain a temperature higher than is due to the heating effects of convection or conduction of or from the hot air or gases.

ing shall be effected substantially exclusively by convection or conduction, and that heatshould be minimized. v

While there is hereinafter described a use '7 of my method and apparatus in a system of stant the temperature of the contents of the control for maintaining substantially conbasket, it shall be understood that my apparatus and method are not limited to employment in such a system, but that my furnace may be operated, so to speak, manually as regards control of the heating current, maintaining, however, the circulation of the air and gases and the reversal, preferably periodically of the direction of circulation. The furnace may be soutilized for any purpose, including, for example, the heat treatment 0f. steel and the like in accordance with the method described in Letters Patent to VVrighton No. 1,188,128, in which case the thermo-couple T, Figs. 1 and 2, disposed within the furnace chamber, may be utilized tr control arecorder, 0f the character indicated in Fig. 4, or equivalent, for drawing a curvein the nature of a time-temperature curve for making observable by inflections of the curve the time when the material passes through a decaleseence stage. By my method and apparatus the various pieces or the entire contents of the basket change in temperature substantially uniformly, ensuring that the curve drawn by the record: ing apparatus represents change of temperature alike in all pieces or contents of the basket.

For controlling the temperature within the h'eatingchamber, as for maintaining it substantially constant, there may be utilized any suitable automatic control mechanism,

one example of which is shown in Fig. 4, illustrating a mechanism of the character 'coil 53 of a galvanometer. In, other words, it 1s preferred that the heatdisclosed in prior Letters Patent of the United States to Leeds No. 1,125,699, supplemented by means for effecting automatically periodic reversals of direction of rotation of i -ries the friction shoes 49, 49 co-acting with the disk 50 secured upon the shaft 51 for 'rotating it in the one direction or the other, depending upon the direction of deflection of the needle or pointe' 52 attached to the The magnitudes of the incren'ients of rotation of the shaft 51 are further detern'iined by the extent of deflection of the needle 52 from its normal or mid position illustrated, all in accordance with the mode of.operatio'n of apparatus of this character, as described in the aforesaid Patent 1,125,699. Secured upon the shaft 51 is the wheel or pulley 54, around-which is wrapped the cord 55 passing over the idler rollers 56 and secured to the pin Ol'll'ltlllfli 57, which draws upon the record sheet or paper Pa time-temperature curve 58. The paper P is fed from the roller 59 by the roller 60, whose teeth engage in marginal perforations in the paper P. The roller 60 is driven by the shaft 61, driven from the shaft 45 through the worm 62, gear '63, shaft 64, worm and gear 66. r

Upon the shaft 51 is secured the disk 67, upon which is disposed the resistance R, with which co-acts the stationary contact 68. The resistance-R is connected in series with the resistance 69, as shown in Fig. 5, adjustable resistance '70 and source of current or battery 71, this circuit forming a portion of a potentiometer; The contact 68 is connected by conductor 72 with the thermo-couple T disposed, as indicated in Figs. 1 and 3. within the heating chamber subjected to the temperature thereof and utilized through the mechanism described for controlling that temperature. The other terminal of the couple T is connected through conductor 73 with one terminal of the galvanometer coil 53, whose other terminal connects through conductor 74 with the terminal 75 of the resistance R, betwee which and the contact 68, for balanced condition of the circuit as effected automatically by the apparatus of Fig. 4, there is a fall of potential equal to the therino-electric motive force developed by the thermo-cou- The two terminals of the resistor 21 are /upon which are secured the three arcuate contacts 77, 77 and 78, co-acting with the stationar contact 79 which connects witlr the conductor a of the two conductors a and 7) of one phase of a sourceof two phase alternating current; "the current of the other and d;

The gap between contacts, 77 and'77 is slight so'that one of them engages brush 79 when the other leaves that brush. The contact 77 connects through the coil 80 of relay Y with the lixed contact 81, adapted tobe brought into communication with the-contact 82, connected with the conductor 7), by the bridging member 8 3, movable with and insulated from the core or movable system 8t energized by the coil 80. The contact 81 is connected with the contacts 82 of a second relay Z having the contact 81 co-acting with the bridging member 83 on core structure 84.. The disc. contact 77connectsthrough the second coil 85 with the contact 86 adapted to be brought into connection with the contact 82 by the second bridging member.-

.87'of'relay Y. The contact. 86 connects also through the magnet winding 88 with the conductor a. Contact 77 connects also thtough the coil 80* of relay Z with the contact 81 adapted to be brought into connection with contact 82% by the bridging me1n-.

ber 83. The .disc contact .78. connects through the coil 85 with the contact 86- andthrough the second magnet winding 88 with the conductor a. 1 I

Eachof the relays-Y and Z is of a character suchthat its core 84 or 84 remains in that position to which lastaattracted by either of, its coils. Y Y Co-actin with the magnet 88 is the armature 89 whlch actuates in unison the movable contacts 90, 91, 92 and 93 co-acting with -stationary contacts connected respectively with the ditlerent conductors of the two: phase supply circuit. A spring-.94 opposes attraction of the armature 89' by coil 88 'and' returns the movable contact members 90-93 to open'cir'euit position when coil 88 1s deener i'zed. The furnace resistor 21 is controlle by movable contacts. 92 and 93 andresistor 22 is controlled by contacts 90 90-93 are in their circuit-closing position ina and 91, whereby when the movable contacts dicated, the resistors 21, 22 are in effect in .parallel on the two-phase supply circuit.

The second magnet .88? when energized attracts its".armature 89 inopposition to;

spring 94 to move the contacts 95, 96 and 97 nto engagement with their co-actin staconnected by conductors 101 and 102 with the-- contacts 109 and .96 -respectively; the

phase is supplied over the conductors .0v

95 and 97 res ectively; and the supply con y su l circuit whereby either hwh or low 1 P y a rate of heating of the furnace effected.

The automat to control system efiects elther high or low rateot heating in the furnace 1 depending upon'tlie position of the contacts 77, 77' and 78 withrespect to the brush 79. As viewed in Fig. 5, the disc 67 is rotated in clockwise direction to effect balance of the galvanometer for increase-0t temperature, and in opposite direction for decrease of ten'iperat'ure. The disc moves with the disc (57 and accordingly for furnace temperature materially below the desired or control temperature the contact 77 is in engagement with the brush 79, and the relays Y and Z are accordingly in such positions that the contacts -93 are in circuit closing position and the contacts 97, of the lower switch, are in open circuit position, and accordingly both resistors21 and 22 are traversed by maximum current, causing. great' est rate of production of heat in the furnace F, causing its temperature rapidly to' rise. As the temperature rises to 'prede I tel-mined magnitude the contact 77- comes switch closed, bringing the two resistors 21 sultant reduced rate of production of heat and 22'into series with each other, with rein the-furnace suflicient however for purposes of effecting the desired or control term perature for which the positlon of the. dlsc 76 is such that the gap between the contacts 77 and 78 is opposite the, brush .7 9. Should the temperature continue to increase, the

disc 76 rotates still further in; clockwise direction, causing contact 78 toenga e'brush 79, whereupon the relays Y and are in such positions that both the upper and Y I I lower switches are open, and neitherof. the resistors 21, 22 isin circuit, w1th the result that production of, heat within the furnace is discontinued. As a result the tem era-- ture will eventually fall, the disc 79 wi l'rotate in counter-clockwisedirection causing contact 77 to engagebrush 79 and brin both resistorsinto series, with resumption o production of heat in the furnace; and simi- I arly should the, temperature nevertheless 'further' -fall, eventually theucontact 77 will engage brush 79 and the resistors will again be. in arallel, further increasing the rate of pro uctionof heat.

When the source of electric current is two phase ,system, as in the example illustrated, the propeller' driving motor M may motor M, the latter is reversed from time to time by reversing the source of connection of the winding 8, for example, with respect to that phase of the supply whose con-- ductors are c and d. This is accomplished by the movable contact levers 109, 110 and 111,

controlled, respectively, by the cams 112, 113

and 114 continuously rotated, as by mounting them upon the shaft 64 of the recorder or controller mechanism. The contact lever 109 co-acts with the contact lever 115, connectcd with the contact lever 111; the contact lever 110 co-acts, respectively, with the contact lever 116, connected to the conduc- 1 pivoted tor a and alternately with the contact lever 117 connected with the conductor d. Similarly, the contact lever 111 co acts with the contactlever 118 connected with the conductor d and alternately with the contact lever '119 connected .to theconductor 0. By this cam-operated switching mechanism described, the sense of traverse of the field winding 108 by the current twice per revolution of the cam shaft 64,

-while the winding 107 is always excited in tending through the shaft into the same sense from conductors a and Z), but its circuit is also opened and closed twice per revolution of the shaft 64 by the cam 120, which actuates the contact lever 121 co-acting with the contact lever 122, the circuit breaking taking place just before closure of circuit through the other winding 108, for purposes of reducing sparking andarcmg. 7

Whether or not the automatic system of recording or control be utilized, the reversal of the motor M as described may be employed.

Furthermore, it shall be understood that the reversal of the fan or propeller may be effected mechanically when the motor 1tself rotates always in the same direct on. This is exemplified in Figs. 6 to 8 inclusive, wherein the rotor of the motor M, revolving always in the same direction drives the rotor shaft 123, upon which is longitudinally movable the hub 124 on the friction disk 125, a spring 126 opposing movement of the disk 125 longitudinally of the shaft 123, though rotated thereby by the pin 127 exa longitudinally extending slot 128 in the hub 124. Upon the hub 124 is disposed the worm thread 129, which meshes with and drives the worm gear 130 secured upon the same shaft with the worm 131, which meshes with and drives the worm gear 132, upon whose shaft is secured the crank disk 133 having the crank pin 134, upon which is the link 135 pivoted at 136 to the link 137, pivoted at 138 to the bracket 139.

is reversed At its one end the lever 137 is bifurcated, and slotted at 140 to receive the pins 141 upon the collar 142 engaging loosely in a groove in the member 143, which is splined for longitudinal movement upon the shaft 144, upon which is secured the fan or blowerdriving pulley 38, for use in arrangements rim 146 also engages the idler friction disk 145, which may yield longitudinally of its axis in opposition to the spring 147.

The friction disk 125 is driven at the speed of the motor M, and effects driving of the shaft 144 through'the friction member 146, movable longitudinally of the shaft 144 from one side of the axis of revolution of the disk 125 to the opposite side, thereby effectmg reversal of the shaft 144. This movement of the member 146 backwardly and forwardly is accomplished by the reduction gearing above described, which operates to move the link 135 upwardly and downwardly and thereby shift the member 146 longitudinally of the shaft 144 across the axis ofdisk 125. In case it is desirable that the transfer from one extreme position to the other of the member 146 shall be effected rapidly, any of the well known quick transfer or snap mechanisms may be utilized, disposed and operating between the crank pin 134 and the lever 137.

While in the example illustrated the source of current for the heaters 21 and 22 is described as polyphase alternating current, itv

tinu'ously rotating staft, which shaft may,

when desired, be a shaft of the recorder or control mechanism, as, for example, the

shaft 64.

It is desirable that the heater or heating element, for example the resistors or resistance elements 21 and 22, shall have low heat capacity in the sense that they are either directly or substantially directly exposed to the air or gas withinthe furnace, or, if imbedded, the mass shall be small enough to store only relatively small amount of heat, or,fshall have a heat capacity which is low as compared with the heat. capacity of the work to be llQiiBd. This low heat ing the heating chamber up to desired or.

[control temperature, or while the control system is in operation for maintaining a substantially constant or predetermined temperature.

For brevity in the appended claims, theterm air is employed generically to include air, gas and vapor within the heating chamber.

As hereinbefore described the circulation of air within the furnace has been forced, as by a blower, fan or equivalent. It will be understood however that the circulation may be that of convection.

For circulation by convection the apparatus may take a form indicated in Figs. t),

10 and 11 wherein the furnace body F is rovided -with a removable cover 18. 'ithin the furnace is disposed the shell 27, within which is the removable basket 28 having the open ring top 29 and the bottom grate 31 upon which the work rests. Upon each of the pivotal shafts 147 is mounted a structure comprising the plates 148 and 149 and'resistance conductors150, which it 7111 be understood may be controlled as are the resistors 21 and 22 hereinbefore described. As indicated in Figs. 9 and 10 there is a passage 151 between the pivot 147 and the outer edge of plate 149 whereby when the parts are in the position indicated in Figs. 9 and 11 the heated air rises from the conductors 150 upwardly through the chamber formed by the members 148, through the basket and its open top 29; thence downwardly outside through the passages 151 and upwardly between the resistance conductors 150. This is a convection circuit effecting uniformityof heatingof the work. The direction of the convection circulation is reversed b moving the arts to the position indicate in Fig. 10, y rotation of the pivotal shafts 147. This ma be accomplished manually or, as

indicate in Fig.'11, by a continuously rotating motor M, which, through suitable reduction gearing, drives a shaft upon which are the cams 152 upon which bear the followers 153 through and by which the shafts 147 are periodically rotated to reverse the direction of circulation. I

What I claim is:

1. In the art of heating materials in a heating chamber, the method which comprises circulating air in the heating chamer to and awayfrom the material to be heated, and reversing the direction of circulation.

2. In the art of heating materials in a heating chamber, the method which comrises circulating air in the heating chamer to and away from the material to be heated, and periodically reversing the di-' rection of circulation. a

3. In the art of heating materials in a heating chamber, the method which comrises circulating air between a source of met in the heating chamber and the material chamber containing material to be heate which comprises increasing the temperature of the chamber toward desired ma itude by a high rateof application of eating agent, simultaneously circulating the air within the chamber, and reversing the di-' rection of circulation.

6. The method of operating a heating chamber containing material to be heated, which comprises increasin the temperature of the chamber toward d e by a 'high rate of application of heating agent, simultaneously circulating the air within the chamber, and reversing the circulation at intervals short as compared with the time required for the heating chamber to {each a temperature of the desired magnituc e.

7. The method of operating a heatin chamber containing material to be ,heate which comprises increasing the temperature of the chamber toward desired ma itude by a high rate of application of eating agent, simultaneously circulating air within the chamber, reversing the direction of circulation, and thereafter applying the heatin a nt at lower rate while continuing said clrculation.

8. The method of operating a heatin chamber containing material to be heatetfi which comprises increasing the tem erature of the chamber toward desired magnitude by a high rate of application of heating agent, simultaneously circulating the air within the chamber, reversing the circulation at intervals short as compared with the time required for the heating chamber to reach a temperature of the desired magnitude, and

thereafter applying the heating agent at lower rate w 1le continuing said circulation.

9. The method of heatvtreating steel or the like, which comprises controlling the temperature thereof while in a heating sired magnitude chamber, circulating the air in said chamber, 21nd reversing the direction of air circulaion.

10. The method of heat-treating steel or the like, which comprises controlling *the temperature thereof while in 'a heating chamber, circulating the air in said chamber, and periodically reversing the direction of air circulation. a

11. The method of heat-treating steel or the like, which comprises controlling the temperature thereof while in a heating chamber, circulating the air in said chamber, reversing'the direction of air circulation, and shielding the steel or the like from absorption of radiant heat.

12. The method of heat-treating steel orthe like, which comprises controlling the temperature thereof while in a heating chamber, circulating the air in said chamber, periodically reversing the direction of air circulation, and shielding the steel or the like from absorption of radiant heat.

13. A furnace comprising a heating chamber adapted to contain material to be heated, a source of heat, means for circulating the air in said chamber with respect to said material'and said source of heat, and means for reversing the direction of the circulation.

14. A furnace comprising a heating chamber adapted to contain material to be heated, a source of heat, means for circulating the air in said chamber with respect to said material and said source of heat, and means for periodically reversing the direction of the circulation. 15. A furnace comprising a heating chamberadapted to contain material to be heated, a source of heat, means disposed between said'source of heat and said material to intercept radiant heat, means for circulating the airin said chamber with respect to said material and said source of heat,'and means for reversing the directionof the circulation.

16. A furnace comprising a heating chamher, a container therein spaced from the wall thereof and adapted to hold material to be heated, said container at one end communicating with the spacebetween it and said heating chamber, an air propeller disposed adjacent an opening at the other end of said container for circulating air thcrethrough and througlrthe space between 'said con tainer and said chamber, and means for reversing said propeller to reversethe direc tion ofcirculation.

17. A furnaee'comprising a heating chamber, a container therein spaced from the 7 wall thereof and adaptedto hold material to be heated, said container at one end communicating with the space between it and said heating chamber, an'air propeller disposed adjacent an opening at the other end of said container for circulating air therethrough and through the space between said contamer and said chamber, a,motor for drivmg said propeller, and means for reversing said motor to reverse the direction of circulation. i i

18. Afurnace comprising a heating chamber, a container within said chamber and spaced therefrom for holding the material to be heated, an electric heater within said chamber in the space between it and said container, means for circulating air through said container and said space, and means for reversing the direction of circulation. 19. The combination with a furnace, of means responsive to the temperature thereof, a source of power, a movable structure, a disengageable connection between said source of power and said movable structure controlled by said temperature-responsive means, means for circulating air in said furnace, and means actuated by said source of power controlling said air-circulating means.- 20. The combination with a furnace, of means responsive to the temperature thereof, a source of power,-a movable structure, a disengageable connection between said source of power and said movable structure controlled by said temperature-responsive means, means for circulating air in said furnace, and means actuated by said source of power controlling reversal of the direction of air circulation.

21. The combination with a furnace, of

means responsive to the temperature thereof, a source of power, a movable structure, a disengageable connection between said source of power and said movable structure controlled by said temperattire-responsive means, means for circulating air in said furnace, a motor for driving said air-circulating means, and means actuated by said source of power for effecting reversals of said motor.

22. The combination with a furnace, of means responsive to the temperature thereof, a source of power, a movable structure, a disengageable connection between said source of power and said movable structure controlled by said temperattire-responsive means, means for circulating air in said furnace, means actuated by said source of power controlling said air-circulating means, and

means controlling the temperature of said furnace controlled by said movable structure.

23. The combination with a furnace, of means responsive to the temperature thereof, a source of power, amovable structure, :1

- disengageable connection between said source of power and said movable structure controlled by said temperature-responsive means, means for circulating air in said furnace, means actuated by said source of power controlling reversal of the direction of air circulation, and means controlling the ioo temperature of said furnace controlled by said movable structure.

24 The combination'with a furnace, of

means responsive to the temperature thereof, a source, of power, a movable structure, .a dise'ngageable connection between said source of power and said movable structure controlled by said temperature-responsive means, means for circulating air in said furnace, a motor for driving said a1r-c1rculatof-said furnace controlled by said movable structure.

, 2?. The combination with a furnace, of

means responsive to the temperature thereof, 7

' ture.

trolled by 'means, means for c1rculat1n air 1n said fur- QGYThc combination .with a furnace, of means responsive to the temperature thereof, a source of power, a movable structure, a

lisengageal)le connection between said source of power and said movable structure con- Sald temperature-responsive nace, means actuated by sai source of power controlling reversal of tie direction of air circulation, and means for recording the temperature of said furnace controlled by said movable structure.

27. The combination with a furnace, of means responsive to the temperature thereof, a source of power, a movable structure, a

mg means,'-'means actuated by said source of power forel l'cctlng reversals of; sald Inotor, and means controlling the temperaturedisengageable connection between said source of power and said movable;-'structure controlled by said temperature-respons1ve means, means for circulating air in said furnace, a motor for'driving said air circulatmg means, means actuated by said source of power for effecting reversals of said m0.-

tor, and means for recording thetempera ture of said furnace controlled by said movable structure. Y

28. The combination with a furnace-having a plurality of electric heaters, ofa tem perature responsive device, and mechanism controlling said heaters and controlled by said temperature responsive device comprismg a movmg system whose positions correspond with different temperatures of said furnace, and'means controlled by said system' for causing productlon of heat at different 4 rates by said heaters for different positions of said system, and means rendermgsaid heaters inoperative for another position of said system. a

29. The combination with a furnace having a pluralityof electric heaters, of a temperature responsive device, a, galvanometer controlled thereby, a source of power, a movable system operated by sa1d source of power 'under the control of said galvanometer, and

switching mechanism comprising relatively movable contacts, one of said contacts causing said heaters to simultaneously produce heat at high rate, another ofsaid contacts rendering said heaters inoperative, and an intermediate contact for brmgmg said heaters into series with each other for effecting heat production at low rate.

In testimony whereof I have hereunto affixed my signature this 19" .day of February, 1925.

JOHN W. HARSCH. 

